Storm water generally refers to water which is generated from precipitation events, while waste water generally concerns water which is generated directly from industrial activity. In both cases, dissolved and suspended heavy metal pollutants are typically present in the water. Both storm water and waste water are discharged to various locations, including sewers, surface discharges such as a ditch, stream or other body or water, or a storm sewer, deep well injection or an infiltration system such as in a detention pond or dry well.
The heavy metals typically present in storm water or waste water, including lead, zinc and copper, are known to have undesirable effects on the environment. As a result, environmental regulatory agencies often place strict limits on the levels of these metals that may be discharged from human activities, such as industrial facilities, as well as public and commercial operations. Current limits for metals in storm water can be as low as 0.014 mg per liter for copper, 0.087 mg per liter for lead and 0.117 mg per liter for zinc, depending on the individual state.
Rainwater is mildly acidic due to the dissolution of carbon dioxide to form carbonic acid. The solubility of metals increases with decreasing pH. As a result, metals exposed to storm water, such as metal fences, can leach directly from the metallic form. As a result, any metal exposure to rainwater can lead to levels of dissolved metals in excess of regulatory limits.
Various techniques have been used for treatment of storm water and waste water, including sedimentation, filtration and constructed wetlands. These usually include a vault-like structure and require significant construction and real estate for implementation. Other techniques include electro-coagulation, adsorption or precipitation. Traditional ion exchange technology has also been employed for the treatment of heavy metals in storm water. All of these techniques, however, require relatively large capital investment, extensive sub-surface construction and/or significant square footage for successful results.
In summary, existing technology for treatment of storm water/waste water is expensive, requiring significant subsurface installation, large amounts of real estate and/or significant capital cost. These are significant constraints for many facilities and geographical areas, and thus make effective treatment of storm water/waste water either difficult or cost-prohibitive in many situations.
Accordingly, it is desirable to be able to reduce heavy metals present in storm water or waste water to acceptable levels, including convenient removal of metals from the dissolved liquid phase, transfer into a solid phase for disposal, recovery or further treatment. Further, it is desirable to have such a treatment system which requires little or no subsurface construction, is portable such that the system can be transported to various sites and can be arranged into a variety of configurations, while requiring less, even significantly less, physical space than existing treatment technologies.